I’ve pushed the dyntopo branch to my github repository, so you can give it a try if you’d like. The code is only about two days old now, so be warned that it’s at a very incomplete stage.
There’s no UI for dynamic topology yet, so as soon as you go into sculpt mode (on a non-multires mesh) it’s active. At some point of course, a switch will be added so you can choose between regular sculpting and dynamic topology.
The detail size is hardcoded at 0.1 BU right now, so you can increase or decrease the mesh density by scaling up or down in edit mode.
Note also that plenty of brushes and features don’t work yet, notably the smooth and grab brushes, as well as undo.
Supporting undo will likely be the biggest challenge for dynamic topology; it’s not at all clear how to store undo data without copying the entire mesh (which would cripple performance.)